This application relates to a repaired gas turbine engine case and method of repair, wherein cold metal transfer is utilized for a replacement weld joint to attach a replacement flange.
Gas turbine engines are known, and include engine cases surrounding several core components. Engine cases typically abut other housing members at flanges, which may then be utilized to connect the engine case to the adjacent housing. The engine cases are subject to a harsh environment during service, and may be damaged. As an example, products of combustion at high temperature pass within the engine case.
Periodically, a gas turbine engine is taken out of service and reviewed for maintenance issues. One engine area that may be subject to repair is the flange of the engine case. In the past, the engine case has been removed, and the existing flange machined away. A replacement flange may then be attached.
At least one known prior art process for attaching the flange generally includes use of an electron beam welding device. However, the devices are expensive to purchase and operate. Also, the devices are vacuum devices that extend repair time because of additional time to pump down a chamber to an acceptable pressure.
A process known as cold metal transfer (“CMT”) developed by the Fronius Corporation has been incorporated into gas metal arc or metal inert gas (“MIG”) welding systems. This process reduces the spatter often associated with MIG welding. This spatter has kept MIG welding from gaining popularity in the aerospace industry.
The term “cold” has to be understood in terms of a welding process. When compared to a conventional MIG/MAG process, CMT is a cold process. Its characteristic feature is alternating hot and relatively cold temperature. This alternating hot and cold treatment occurs by incorporating a welding wire motion into a process control.
The wire moves forward and into a weld pool. A short circuit occurs. As the short circuit happens, the wire is pulled back again. In this way, a weld arc only inputs heat very briefly in the arcing period, after which the thermal input is immediately reduced. In this way, the alternating hot and cold occurs.
The rearward movement of the wire assists weld material droplet detachment during the short circuit. The short circuit is thus controlled and kept small.
CMT has not been utilized in repair applications for gas turbine engine cases.